1. Field of the Invention
The present invention pertains to a separator for use in separating oil from oily water. The oil/water separator is particularly useful in industrial manufacturing plants where oil-contaminated water is produced by manufacturing processes such as molding operations, lubricating applications, machining operations, etc.
2. Background Art
Separation of oil from oil-contaminated water has long been problematic in numerous fields. In oil production, for example, the recovery of oil is generally accompanied by recovery of water at the same time. In wells where recovery proceeds by secondary or tertiary methods, the major portion of liquid may be water rather than oil. Following separation of the bulk of the oil from the recovered liquid in these processes, the water which remains is highly contaminated by oil, and thus cannot be disposed of without environmental concerns.
In manufacturing, removal of mold releases when cleaning molds, oil spills, dripping of lubricating oils and greases from conveyor belts, leakage of oil from hydraulic systems, and machining operations are but a few examples of oil loss which may end up as oil-contaminated water. Oily water which contains less than 100 ppm oil can be processed by conventional sewage plants, and thus may be disposed of relatively economically in this fashion, incurring but a modest sewage treatment cost. However, it is desirable from the standpoint of environmental stewardship to have as low an oil content as is reasonably economically possible.
For oily water with higher oil content, disposal is most problematic. In at least some areas of the United States, oily water disposal costs may run as high as $1.50/gallon ($0.40/l). For manufacturing plants which can easily produce 2000-3000 gallons of oil water per month, annual disposal costs are quite high. Recycling of the oily water without treatment is not practical, as the oil content continues to increase. Moreover, the relatively high levels of oil result in fouled process equipment which requires shut down and cleaning, or even replacement.
Separation of oil and water mixtures at the site of its production has been in use for many years. Older methods of separating required long periods of quiescent standing in large settling tanks, or use of special surfactants to destabilize oil emulsions. While such processes may be used with very heavy contamination such as that encountered in oil production, they are inefficient and not cost effective at lower oil contamination levels when used alone. Moreover, the water effluent is still likely to contain undesirable oil levels, i.e. levels greater than 100 ppm.
Mechanical separators have been in widespread use for many years. While such separators may take a variety of forms, including portable separators, virtually all require special coalescer plates or replaceable cartridges containing such plates. The coalescer plates are composed of or covered with a hydrophobic substance to which the oleophilic oil droplets are attracted, and coalesce. The plates are of limited surface area, and generally require a non-turbulent, laminar flow. The laminar flow prevents efficient separation, as oily water in the center of the flow path may pass through such devices without contacting the plates; thus, the oil mass transfer coefficient is low. Moreover, because of the need to produce cartridges with many closely spaced but separated plates, manufacturing costs of the coalescer cartridges and replacement cartridges is high. Examples of such oil separators employing parallel coalescer plates or equivalent devices are those described in U.S. Pat. Nos. 4,072,614; 4,149,973; 4,199,451; 4,333,835; 4,722,800; 5,296,150; 5,520,825, and 5,928,524. Finally, existing oil separators tend to be very expensive, and often must be operated either at very low flow rates or connected in series to provide oil separation to below 100 ppm oil in the aqueous effluent. Many of these separators are incapable of separating emulsified oil.
It would be desirable to provide an oil and water separator which is itself inexpensive, which employs an inexpensive oil separation means, and which is efficient in separating oil to levels considerably below 100 ppm. It would further be desirable to provide an oil and water separator which can be used at reasonable flow rates without impeding separation efficiency, and which is capable of separating oil even from oil/water emulsions.
It has now been surprisingly discovered that a highly efficient and cost effective oil separator may be constructed which is effective to remove oil to levels well below 100 ppm without employing parallel coalescer plates and laminar flow. The oil/water separator comprises a hollow elongate housing having an oil/water inlet mediate an oil outlet and an effluent outlet, the hollow elongate housing filled with hydrophobic polymer beads or granules or hydrophobic polymer coated beads or granules.